1. Field of the Invention
The present invention relates to a wafer attaching method of attaching a wafer having a warp to a sheet.
2. Description of the Related Art
A wafer to be used in manufacturing semiconductor devices is formed by slicing a solid cylindrical ingot of silicon, for example, by using a wire saw. The wafer thus obtained by slicing (as-sliced wafer) has a warp due to the processing accuracy of the wire saw. It is difficult to accurately form semiconductor devices on such a wafer having a warp, and it is therefore necessary to remove the warp by any method such as grinding, thereby planarizing the wafer. However, when the wafer is held under suction on a chuck table of a grinding apparatus, the wafer is deformed by a suction force to temporarily lose the warp. Accordingly, the warp cannot be properly removed by grinding. To cope with this problem, there has been proposed a method of attaching a wafer having a warp to a film (sheet) in the condition where the warp is maintained (see Japanese Patent Laid-open No. 2009-148866, for example).
In this method, a liquid resin curable by light such as ultraviolet light is applied to the wafer, and the wafer is next pressed against the flat film. Accordingly, the wafer is deformed by the pressure against the film, and the resin is spread over the entire contact area between the wafer and the film. Thereafter, the pressure applied to the wafer is removed to restore the warp of the wafer. Thereafter, light is applied to the resin to cure the resin, so that the wafer is fixed through the cured resin to the film in the condition where the warp is maintained. In this manner, the wafer is attached to the film in the condition where the warp is maintained, thereby allowing proper removal of the warp by any method such as grinding.